The present invention relates to the surface marking of a solid substrate, for example one made of glass.
It is currently still difficult to surface mark glass substrates, for example the outer surface of a container or a bottle, with traditional equipment, for example by flexography or pad printing. Screen printing also needs drying and/or baking operations, requiring complex and expensive equipment. This method is still relatively slow and leads to production costs which are often unacceptable.
There are a variety of factors which in practice make it difficult to obtain durable marking with such means:
the glass surface remains slippery;
the printing ink or inks adhere poorly to the surface, so that any friction is liable to remove the marking at least partially.
It is further known to mark the surface of a solid substrate, for example one made of plastic, by engraving, using a laser instrument for this purpose, that is to say a beam of coherent monochromatic light. Such a printing technique does not necessarily lead to marking which has high contrast and can consequently be read properly with the naked eye. In order to improve contrast, in the case of a plastic, it has been proposed to incorporate reactive particles into its surface. This often leads to degradation of the quality of the plastic.
The present invention relates to a method and to an installation for surface marking a solid substrate, allowing any suitable symbol to be reproduced readably and durably on the surface of said substrate.
The term xe2x80x9csurface markingxe2x80x9d means a form of marking which modifies or alters the surface of the substrate into the latter but over a very limited thickness, corresponding to simple abrasion.
According to the present invention, a surface marking method successively combines an exposure sequence and a sequence of targeted projecting of printing medium.
During the exposure sequence, the substrate is exposed to coherent monochromatic light, or laser light, in order to strip the substrate over a continuous or discontinuous indented surface, under conditions, including duration, such that the indented surface is restricted to simple abrasion, designed and sufficient to contain and bond the printing material which will be discussed below. This means that the conditions or parameters of the exposure are chosen, as regards their respective values, in a way which is sufficient to strip the surface of the substrate but without eroding it to the extent of obtaining a permanent engraving. In the context of the present invention, the exposure does not make it possible to obtain engraving which is on its own sufficient for permanent marking of the substrate.
Next, during the sequence of targeted projecting in discrete form, particles of the printing medium, the deposition of which subsequently defines a printed element, are projected into the indented surface obtained after the exposure sequence.
As regards the projecting sequence, there are two different embodiments to consider:
the projecting sequence is carried out in liquid form, by virtue of which the particles are droplets in liquid form, the deposition of which defines a printed element, in particular after fusion and setting, or drying;
the projecting sequence is carried out in solid form, as a powder, by virtue of which the particles are grains, in solid form or as a powder, the deposition of which defines a printed element, after adhesion to the substrate.
Preferably, according to traditional printing techniques employing a frame, the symbol to be marked or reproduced is predetermined by the juxtaposition or combination of points, having identical or different elementary areas. According to the present invention, each point corresponds to one element printed using the method defined above, having identical or different elementary areas.
Accordingly, a surface marking installation according to the invention consists of the interaction of the following means, namely:
an instrument for exposing the substrate to coherent monochromatic light, comprising a source of said light, a head for projecting a beam of said light, and a component for controlling said beam, in particular its modulation and/or its orientation in space;
an instrument for projecting in discrete form targeted onto the substrate, comprising a source of the aforementioned printing medium, a head for projecting a jet of particles of the printing medium, and a component for controlling said jet, in particular its orientation in space and/or the size of said particles;
means for moving the substrate relative to the head for projecting the beam and the head for projecting the jet, or vice versa;
a control means which is connected to the components for controlling the beam and the jet and is designed to obtain on the substrate as a function of its position relative to the heads for projecting the beam and for projecting the jet respectively, simple abrasion designed for bonding of the printing medium then deposition of the latter, targeted into the indented surface, successively at the same point having elementary area, all the points coated with the printing medium, or printed points, in combination representing a symbol with which the substrate is thus marked.
The present invention has the decisive advantage of decontaminating the surface layer of the substrate, by virtue of the use of the laser beam, which makes it possible to obtain a perfectly clean and decontaminated indented surface before printing. Such an advantage is significant in industries such as the pharmaceutical industry, in which there is always a desire for supports having a maximum decontamination level.
According to FIGS. 1 to 3 described below, three embodiments of the invention may be employed:
according to FIG. 1, the indented surface 3 of the substrate 1 is matched to or larger than the area circumscribing the symbol 4 to be reproduced or printed; the indented surface is then coated, point by point, with particles 6 of the printing medium in order to obtain, as represented in FIG. 1, printed points whose combination represents the symbol 4;
according to FIGS. 2 and 3, the symbol to be reproduced is defined by the juxtaposition of printed points 7 which have equal elementary area and are assembled in a predetermined pattern corresponding to the symbol 4; during the exposure sequence, the substrate 1 is moved relative to the beam of coherent monochromatic light, or conversely by deviating the beam; this beam, obtained for example with a so-called dot matrix CO2 laser, is pulsed, in order to define a plurality or multiplicity of indented points 31, the combination of which represents the symbol 4; then, by moving the substrate 1 relative to the jet of particles of the printing medium, or conversely by deviating the jet, only the indented points 31 are coated with the particles 6 of the printing medium in order finally to obtain, as represented in FIG. 2, printed points 7 whose combination represents the symbol 4;
according to FIG. 6, the indented surface 3 obtained at the end of the exposure sequence is identical to and reproduces the symbol to be reproduced, while being limited by one or more continuous and/or discontinuous lines; then during the projecting sequence, the indented surface is coated, point by point, with the particles 6 of the printing medium in order finally to obtain, as represented in FIG. 2, printed points 7 throughout the indented surface 3.
The elementary 31 and overall 3 indented surfaces which are represented in FIGS. 1 and 6 can be obtained in several ways, namely:
with a relatively wide-section laser beam which passes through a mask and whose energy density is tailored to the marking dimensions; for example, a TEA (Transverse Excited Atmospheric Pressure) pulsed CO2 laser seems well-suited for such a method;
with a laser beam deflected and driven by computer along two perpendicular axes; for example, a CW (Continuous Wave) laser seems well-suited for such a method;
these two methods may themselves be employed, where appropriate, according to a so-called dot matrix technique, for example with a CO2 laser.